1/244 Nolan St, Unanderra NSW 2526
This code is common when a larger exhaust has been fitted or other modifications have been carried out, however it can occur on completely stock vehicles.
P1251 is most often defined as... "Stepper motor intermittent"
Where in fact this code is an over boost code, the stepper motor gets the blame as its in control of the VNT and therefore the boost control.
How the system works:
In the lower load levels, the ECU does not ‘close loop boost control’. Basically, the ECU has a predetermined ‘VNT position’ table based on the loads. This dictates ‘roughly’ the boost levels, and given the low loads, close enough is seen as good enough. When the load levels come up, the ECU gets into its closed loop, and therefore will do whatever is required to maintain its ‘target boost levels’.
Common causes of P1251:
Basically, anything that causes the engine to produce more boost than it should. some examples are:
High flow exhaust added
This is one of the most common 4wd upgrades done and therefore one of the higher contributors to these issues.
Piggyback chip
As a piggyback chip is designed to ‘trick’ the ecu, there ends up being more fuel than the ECU knows about and thus creates more exhaust gasses which in turn ‘over spool’ the turbo.
*This is NOT the case for remap!
Higher flowing injectors / nozzles
For the same reason above!
Failed Stepper motor
Due to the failing stepper motor, it holds the VNT in the incorrect position and causes the issue.
Failed Turbo
Least commonly of all, the actual VNT assembly itself has failed or become physically seized within the turbo.
Please call us direct for further free tech support 1800 465 328.
I hope you enjoy reading this blog post.
Baileys Diesel Group offers free tech support from qualified mechanics and an online store for all your diesel requirements including world-class diesel injectors for unparalleled performance, delivered Australia-wide.
I hope you enjoy reading this blog post.
Baileys Diesel Group offers free tech support from qualified mechanics and an online store for all your diesel requirements including world-class diesel injectors for unparalleled performance, delivered Australia-wide.
With over 48 years expertise and knowledge the Baileys Diesel Group is an industry world leader in diesel combustion efficiency and technology.
To assist clients to reduce all fuel consumption by applying efficient diesel combustion whilst reducing carbon emissions, and therefore reducing environmental and social impacts.
Environmental: actively reduce greenhouse gases and emissions. Ethical: consistent application of strong moral and ethical principles. Commitment: measure, compare, improve and validate. Efficiency: innovate in all areas of development, technology and manufacturing. Operations: support sound project management and methodology principles.